The interchange of freight from one mode of transportation to another, e.g., from road to rail and vice versa, is costly and logistically tedious. The advent of intermodal containers has simplified the process since they are designed to move freight from one mode of transport to another without unloading and reloading the contents of the container. In common use are semi-trucks suitable for transporting intermodal containers via semi-trailers. Railcars suitable for transporting semi-trailers have been developed and are generally known as articulated flat cars. A simple method of transporting semi-trailers over rail is simply by “piggy backing” or loading the semi-trailers onto flat bed railcars.
Articulated flat cars can differ from conventional railcars in a variety of ways, e.g., in not being as heavily constructed since the semi-trailer loads are relatively light compared to loaded box cars, in having different forms of connectors between cars, and often in being constructed at each end so as to form a continuous pathway from car-to-car for circus style loading of semi-trailers. In circus style loading, semi-trailers are attached to a yard tractor or hostler and backed onto a first railcar and then along a series of articulated cars until reaching a final position.
Conventional loading and unloading of semi-trailers individually and sequentially from flat bed railcars occurs by lifting them each by crane and moving them to a desired location, on or off the flatbed railcar. This Lift On-Lift Off procedure of special liftable semi-trailers is achieved by expensive travelling gantry cranes or by expensive heavy-duty lift trucks loading and/or unloading liftable semi-trailers one-at-a-time along the length of the train.
In recent years a variety of systems for non-lifting road to rail horizontal interchanges of semi-trailers have been promoted. One system of interchanging standard semi-trailers between road and rail requires a very complex in-terminal mechanism to unlock a single railcar from within a train and to rotate the disconnected section across the railway to permit a semi-truck to enter/exit diagonally onto or off of the railcar. An alternative method has been proposed to perform the elevation and rotation of moveable railcar floors of railcars in the manner detailed in European Patent No. 0 453 537 whereby standard non-liftable semi-trailers are loaded on and unloaded from railcars by Roll On-Roll Off mode. In this instance, a rail freight terminal is equipped with a series of ‘Pop-Up’ mechanisms secured centrally between the rails of railway foundations, powered to raise; rotate, and lower the underside of moveable wellfloors to rest on the platform edges diagonally across the railway. This method requires the coordination of the wellfloor properly positioning the arriving semi-trailer with the waiting tractor on one side of the railway, and alignment with departing tractor and departing semi-trailer on the opposite side of the railway.
It is therefore desirable to provide improvement in the efficiency of loading and unloading freight from railcars.